Moon Watch

The Moon is a thin waxing (growing larger) crescent. First quarter is next Wednesday, Sept. 27.

Autumn officially begins at 1:02 p.m. Friday, Sept. 22, Tucson time. At that very moment, the Sun shines directly on the equator briefly as it goes from the northern part of the sky to the southern part of the sky.

Actually, the Sun’s apparent movement through the sky is due to the Earth’s motion around the Sun. The tilt of the Earth’s axis with respect to its orbital plane around the Sun gives the appearance of the Sun being in the northern part of the sky from the vernal (spring) equinox around March 21 until the autumnal equinox around Sept. 21.

On Thursday, Sept. 21, look at the western sky at 6:45 p.m. The 2-day-old crescent moon will be 9 degrees above the horizon. Five degrees to the left (south) of the Moon is bright Jupiter, which is getting ready to leave our evening sky for a while. If conditions are really good, and you have a clear horizon, you may even see Spica the brightest star in Virgo the Virgin hovering along the western horizon 4 degrees below Jupiter.

Next Tuesday night the nearly first quarter Moon will be almost directly south after sunset. That night it is just 2 degrees above Saturn, which itself is about halfway between Scorpius the Scorpion to the right (west) and Sagittarius the Archer to the left (east). Fall nights are usually clear, and this fall starts off with a lot to see.

Tim Hunter is an amateur astronomer who has written this column since 2007. He can be reached at akyspy@tucson.com